Gearing Question

[Jonnny]

If my bike is fitted with a 12-28 rear cassette.. I feel it's fine for hills, but for flat/downhill I feel I could do with another gear.

Would I need a higher number or lower number for more speed?

12-30 or 12-25?

[z4chris99]

11-28...

if your spinning out a 12 you need an 11.

what's upfront?

I have 39/53 and 11-25 or 11-28 if it's hilly, think it's fine

[Mr Will]

Jonnny said:

If my bike is fitted with a 12-28 rear cassette.. I feel it's fine for hills, but for flat/downhill I feel I could do with another gear.

Would I need a higher number or lower number for more speed?

12-30 or 12-25?

Neither. The second number of the pair is your lowest/easiest gear. You need to change the first number instead, to an 11- (there aren't any smaller than that).

What are your gears at the front though? They make just as much difference.

[47p2]

If you have a compact gear on the front the big ring will be 50T

so here is the lowdown on gear sizing for 50T, 52T and 53T


50T-12 = 109.6 gear inches...Speed at 101rpm = 33mph
50T-11 = 119.6 gear inches...Speed at 102rpm = 36mph

52T-12 = 114.0 gear inches...Speed at 100rpm = 34mph
52T-11 = 124.4 gear inches...Speed at 102rpm = 38mph

53T-12 = 116.2 gear inches...Speed at 100rpm = 36mph
53T-11 = 126.8 gear inches...Speed at 100rpm = 38mph

[upsidedownmark]

Realistically, if you're 'spinning out' on the flat, you either a) need to work on spinning faster, or b) apply for a job with a pro team..

I can pedal up to 70kph (whatever that is in miles) with 50 front 12 rear (i.e. quite short gearing) as my biggest gear. Admittedly that's at the limit of how fast I can spin, but there are gears to spare on the flat at 40kph, and if I'm over 60kph (i.e. downhill), it's a good time to do some recovery for when I have to go back up.

Without knowing you, I'm going to guess that you're grinding too big a gear and you'd go better and longer if you up the cadence (leg turnover) some. Or you're on a mountainbike

[nammynake]

As above spin faster. No way you're spinning out 50-12 on the flat.

[Rich_W]

47p2 said:

If you have a compact gear on the front the big ring will be 50T

so here is the lowdown on gear sizing for 50T, 52T and 53T


50T-12 = 109.6 gear inches...Speed at 101rpm = 33mph
50T-11 = 119.6 gear inches...Speed at 102rpm = 36mph

52T-12 = 114.0 gear inches...Speed at 100rpm = 34mph
52T-11 = 124.4 gear inches...Speed at 102rpm = 38mph

53T-12 = 116.2 gear inches...Speed at 100rpm = 36mph
53T-11 = 126.8 gear inches...Speed at 100rpm = 38mph

How do you work that out? Been trying to do an equivalence to another bike

Chainring x sprocket x wheel size?

[Magic919]

http://sheldonbrown.com/gears/

Calculator on there will do it.

[okgo]

nammynake said:

As above spin faster. No way you're spinning out 50-12 on the flat.

Or buy an 11. Not everyone wants to spin at 101 rpm to get 33mph!

[upsidedownmark]

Yes, but:

Unless you're a 4XX watt FTP time trialling monster, 33mph is out of reach of most recreational, and even a lot of enthusiast cyclists, unless on a pretty big descent.

If you ARE the sort of person who puts out the watts to regularly see those sort of speeds, the chances are that you a) know enough about what you need to not be asking on the bike sub-forum of a motoring site, or b) have a coach etc who can tell you what you need to do.

The balance of probability therefore suggests that the OP is grinding along at a very low cadence, Hence the entirely well meant advice that he/she probably needs to work on spinning at a higher cadence, to the benefit of their endurance, knees, speed etc.